Electrical screw spindle coolant pump

ABSTRACT

An electrical screw spindle coolant pump is suitable for conveying a coolant circuit or other corrosive, liquid media. The electrical screw spindle coolant pump has a spindle housing with a spindle chamber and an axially adjacent motor housing. The motor housing has a motor chamber, in which a dry-running electric motor is arranged separated from the flow current. The motor housing has a thermal transition portion through which the flow current flows. The thermal transition portion is arranged between the motor chamber and a component boundary of the motor housing to the spindle housing.

The present invention relates to an electric coolant pump of the screwpump type for delivery of a coolant circulation or the like, inparticular for delivering corrosive, liquid media.

Screw pumps are displacement pumps which permit high pressures and highvolumetric efficiency. They do not offer adjustment of the geometry in amanner independent of speed but they do comprise a robust rotary pistonmechanism which is not sensitive to fouling and which operates withoutdelicate elements such as stop valves or the like. Consequently,mechanically driven screw pumps have to date predominantly been used inlarge-scale applications such as e.g. oil pumps in stationaryinstallations or ships engines in which they run with relativelyconstant operating points.

In the area of fuel delivery pumps of vehicles, smaller electricallydriven screw pumps have recently become known, these permitting higherpressures than centrifugal pumps. These are installed in a submergedarrangement in the vehicle tank and provide a high input pressureupstream of the high-pressure pump or injection pump in the fuel path.The electric drive of such fuel delivery pumps is designed as awet-running electric motor without a separating can and so both therotor and the stator are in contact with the fuel. The temperature ofthe fuel delivered from the tank generally corresponds to an ambienttemperature of the vehicle. As a result, the drive, which heats up owingto electric power dissipation, is easily cooled in such fuel deliverypumps.

Thus US 2018/0216614 A1 describes a screw pump which is provided as afuel pump. A cover with an axial outlet is attached to a housing of thescrew pump. The electric motor is received in an outlet chamber of thecover and fuel flows through it before it leaves the outlet.

DE 10 2015 101 443 B3 describes a fuel pump with a housing in which anelectric drive motor is coupled to a screw pump. The fuel flows throughthe drive motor before it leaves the pressure-side outlet.

WO 2014/138519 A1 describes an electric liquid pump of the screw type.The liquid which flows through an inlet and an outlet also surrounds themotor. A fuel is mentioned as the liquid. A flange plane, which is shownin the illustrated construction between a motor-side housing part and apump-side housing part, extends between the motor and a pump-sideoutlet.

DE 10 2017 210 771 A1 describes an electrically driven screw pump as afuel delivery assembly. A pump housing and an electric motor arereceived in a casing. In the illustrated embodiment, which does notcomprise a separating can on the stator of the electric motor, theelectric components of the motor are in direct contact with the fuelwithin an outlet guide on a pressure side of the spindle chamber.

However, the above-mentioned pumps cannot be transferred to anapplication as an electric water pump, in particular not as an electriccoolant pump. A liquid medium to be delivered, such as a coolant wouldcorrosively damage the exposed components of the electric motor, inparticular the coil windings of the stator.

U.S. Pat. No. 6,371,744 B1 describes an electric vacuum pump of thescrew type. The screw spindles are driven by an electric motor which isarranged in a separate housing.

Independently of specific modifications between a screw pump for gassesand a screw pump for liquids, said vacuum pump could not be transferredto an application as an electric coolant pump. In the case of theillustrated arrangement, sufficient cooling of a dry-running electricmotor could not be ensured. In a pressurised coolant circulation, atarget temperature for a coolant can be in the vicinity of the boilingtemperature of the coolant. In this case, in continuous operation,overheating damage to electric or electronic components would occur.

On the basis of the known electric screw pumps of the prior art, whichare not suitable for an application as a coolant pump, it is an objectof the present invention to provide an electric screw pump which issuitable for delivering corrosive, liquid media and provides cooling ofthe electric drive.

Another, partial aspect of the object is further to provide acorresponding technical solution such that it can also be inexpensivelyproduced in large numbers by mass production.

The object is achieved by the features of claim 1. The electric screwcoolant pump in accordance with the invention for delivering a coolantcirculation is characterised in particular in that a motor housingcomprises a motor chamber, in which a dry-running electric motor isarranged in such a manner that it is delimited with respect to thedelivery flow; and that the motor housing comprises a heat transfersection, through which the delivery flow flows, arranged between themotor chamber and a component boundary between the motor housing and aspindle housing.

Therefore, for the first time, the invention provides a screw pump as acoolant pump.

Furthermore, for the first time, the invention provides a screw pump asan electric liquid pump which is driven by a dry-running electric motor.

Furthermore, for the first time, the invention provides a screw pump asan electric liquid pump, in which a convection-assisted heat transferfrom a dry motor chamber to a delivery flow of the liquid medium to bedelivered is provided.

The invention permits a coolant pump to be produced with a high level ofpower density. The screw pump provides the high delivery pressure of adisplacement pump but with relatively low pulsation, similar to acentrifugal pump. In connection with an electric drive, the screw pumppermits universal installations and applications. The electric screwcoolant pump in accordance with the invention is suitable e.g. for usein electric, in particular battery-electric, vehicles, in which nomechanical drive source is provided, and a branched structure of thin orcapillary cooling ducts in a battery module or a traction motor requiresa high delivery pressure.

From a constructional point of view, the invention is based on aprinciple of shifting an axial position of a component boundary betweena motor housing and a spindle housing from a conventional functionalposition further in the direction of the spindle chamber. In this way,on the one hand, a region protected from the liquid of the delivery flowis provided and so the electric drive is not exposed to corrosiveinfluences. On the other hand, by reason of the heat transfer section, aliquid-carrying region on the motor housing is provided, which enlargesan internal thermal contact surface with the coolant. Waste heat fromelectric power dissipation can be effectively carried away from the pumpby a heat exchange at the thermal contact surface, thus produced, of theheat-conducting motor housing and convection of the delivery flow, evenwhen there is a small temperature difference between the electric driveand the coolant.

The enlargement of the thermal contact surface is achieved without anincreased level of complexity in the structure, as in the form ofsurface-enlarging structures, flow resistance means or the like. Themotor housing is designed as a cast part during product development. Asa result, the changed component boundary can be produced on the pumpconstruction in accordance with the invention without considerableoutlay or increase in manufacturing costs. By reason of shifting thecomponent boundary of the spindle housing in a complementary manner,substantially no disadvantageous increase in the overall dimensions ofthe pump arises despite having an increased axial dimension for themotor housing.

Flow losses in the pump are considerably reduced in comparison with aknown pump construction with a wet-running electric drive which isexposed in the delivery flow.

The above-mentioned shifting of the component boundary leads to an openspindle chamber cross-section at the end of the spindle housing. Thusthe screw spindles can simply be inserted through the open end of thespindle chamber during assembly of the pump.

Advantageous developments of the invention are provided in the dependentclaims.

According to one aspect of the invention, the heat transfer section canfurther comprise the pump outlet. In this way, the flow cross-section ofthe entire delivery flow can be channelled past the motor chamber. Theinternal surface of the pump outlet at the heat transfer section furtherenlarges the thermal contact surface of the heat-conducting motorhousing with the delivery flow to a considerable extent.

According to one aspect of the invention, the heat transfer section cancomprise a delivery flow chamber which produces a connection between thefrontal delimitation of the motor chamber and the spindle chamber. Bythis design, the heat transfer portion of the heat-conducting motorhousing between the electric heat sources in the motor chamber and thedelivery flow is shortened further. Furthermore, the internal surface ofthe delivery flow chamber in the heat transfer section further enlargesthe thermal contact surface of the heat-conducting motor housing withthe delivery flow.

According to one aspect of the invention, the heat transfer section cancomprise a bearing seat for a shaft bearing, which is arranged betweenthe electric motor and the screw spindles. The surface of the bearingseat in the heat transfer section in turn enlarges the thermal contactsurface of the heat-conducting motor housing with the delivery flow.Moreover, the integration of a shaft bearing in the axial region of theheat transfer section is favourable to a compact construction for thepump.

According to one aspect of the invention, an electronic system for theelectric motor can also be arranged in the motor chamber. A further heatsource is therefore incorporated into the inventive cooling of theelectric drive. In this way, the power dissipation from powerelectronics is also discharged via the delivery flow.

According to one aspect of the invention, a stator and/or an electronicsystem of the electric motor in the motor housing can be in contact witha frontal delimitation of the motor chamber. Therefore, the smallestpossible heat transfer portion of the heat-conducting motor housingbetween the electric heat sources in the motor chamber and the deliveryflow is ensured.

According to one aspect of the invention, the heat transfer section canbe formed integrally with the motor housing. In this way, an optimisedheat transfer portion without boundary surfaces or joints in thematerial and the lowest possible production costs for the motor housingare ensured.

According to one aspect of the invention, the spindle housing can beformed as one piece. As explained above, the shifting of the componentboundary between the motor housing and the spindle housing produces anopen cross-section for the spindle chamber. In this way, both forassembly of the pump and also for production of the moulded body of thespindle housing no division into two housing halves is required. Theone-piece design of the spindle housing ensures a joint-free internalcontour for the spindle chamber without the need for post-processing.The internal contour of the spindle chamber can be produced simply andprecisely by bores.

According to one aspect of the invention, the spindle housing cancomprise the pump inlet. The spindle housing is designed as a cast partduring product development. Consequently, by integration of the pumpinlet, the number of components of the pump construction in accordancewith the invention can be reduced without considerable outlay.

According to one aspect of the invention, a flange joint consisting of aflange section of the motor housing and a flange section of the spindlehousing can be formed at the component boundary between the motorhousing and the spindle housing. The flange joint permits a preferredscrew connection for assembly of the two housing components, while acorresponding flange plane allows different types of seal.

The invention will be explained hereinafter with the aid of anembodiment and with reference to the accompanying drawing,

FIG. 1 shows a schematic sectional view through a screw coolant pumpaccording to one embodiment of the invention.

In terms of this disclosure, the term ‘screw pump’ is understood to meanskew rotary piston pumps with a thread pitch for displacement of themedium to be delivered. Such types of pump generally comprise a drivenscrew spindle 2 a and at least one further screw spindle 2 b which is incoupled motion therewith via engagement of the toothing.

In the embodiment of the schematic illustration of FIG. 1, in a spindlehousing 1, a driven screw spindle 2 a and a screw spindle 2 b in coupledmotion are received in a rotatably mounted manner in a spindle chamber10 of the spindle housing 1. The spindle chamber 10 has across-sectional contour in the form of a so-called figure-of-eighthousing, i.e. it is formed by two bores in the pump housing 1 withoverlapping radii in order to ensure engagement of the screw spindles 2a, 2 b. The driven screw spindle 2 a is connected to an electric motor4.

A pressure side of the spindle chamber 10 which communicates with a pumpoutlet 13 in the form of a pressure connection is located on the driveside of the screw spindles 2 a, 2 b. A suction side of the spindlechamber 10 is located on the other side of the screw spindles 2 a, 2 bopposite the electric motor 4. The suction side of the spindle chamber10 communicates with a pump inlet 11 in the form of a suctionconnection. In relation to the delivery direction of the screw pump, aliquid medium to be delivered or a coolant is drawn into the spindlechamber 10 from a coolant circulation through the pump inlet 11 on thesuction side. A rotational movement of engaged screw profiles of therotating screw spindles 2 a, 2 b generates a negative pressure on thesuction side of the spindle chamber 10 and a positive pressure on theopposing pressure side of the spindle chamber 10. The medium to bedelivered is delivered by continuous displacement along a screw pitch ofthe engaged screw profiles and ejected from the spindle chamber 10through the pump outlet 13.

A motor housing 3 adjoins the spindle housing on the pressure side ofthe spindle chamber 10. The motor housing 3 comprises a flange section35 which is formed to match a flange section 15 of the spindle housing1. The flange joint is sealed by a seal. A separated motor chamber 30 isformed in the motor housing 3, in which chamber the dry-running electricmotor 4 and an electronic system, in particular power electronics (notshown), for switching the electric power at the electric motor arereceived. An open end of the motor chamber 30 is closed by a motor cover(not shown). A collar-shaped bearing seat 32 with a though-opening in afrontal delimitation of the motor chamber 30 is formed in the motorhousing 3. A common shaft bearing 23 of the electric motor 4 and of thedriven screw spindle 2 a is fitted in the bearing seat 32. Upstream ofthe shaft bearing 23, a shaft seal 34 is fitted into the bearing seat 32and seals the motor chamber 30 against ingress of liquid.

The dry-running electric motor 4 is of the internal rotor type with aninternal rotor 42 and an external stator 41. The rotor 42 is coupled tothe driven screw spindle 2 a. The stator 41 comprises field coils whichare actuated by the power electronics and supplied with electric power.The stator 41 of the electric motor 4 is in thermal contact with aninternal peripheral surface and with a frontal boundary surface of themotor chamber 30, and so waste heat from the field coils of the stator41 is transferred to the motor housing 3.

The motor housing 3 consists of a metallic material with a good level ofheat conductivity, such as an aluminium cast alloy, and is formed as aone-piece cast part. A heat transfer section 31 of the motor housing 3extends in an axial section between the motor chamber 30 and the flangesection 35. As an integral component of the heat transfer section 31,the pump outlet 13 in the form of a radially discharging pressureconnection is arranged between the motor chamber 30 and the spindlechamber 10. A delivery flow chamber 33 is formed within the heattransfer section 31 and has the liquid medium to be delivered flowingthrough it. The delivery flow chamber 33 produces a connection for thedelivery flow of the pump between the pressure side of the spindlechamber 10 and the pump outlet 13. The delivery flow chamber 33surrounds the collar-shaped bearing seat 32 and carries the pressurisedliquid medium to be delivered to the frontal delimitation of the motorchamber 30, with which the stator 41 is in thermal contact.

The heat transfer section 31 constitutes the region of theheat-conducting material volume on the motor housing 3 which isdefinitively involved in the dissipation of waste heat from the motorchamber 30 into the delivery flow. The internal surface of the pumpoutlet 13, the internal surface of the delivery flow chamber 33 and thesurface of the bearing seat 32 each contribute to enlargement of thethermal contact surface between the motor chamber 30 and the deliveryflow within the heat transfer section 31.

The optimised heat transfer limits any temperature difference between acoolant and the motor chamber 30. Consequently, even under high loadingwith a high operating temperature in a coolant circulation, a criticalcomponent temperature of the electric drive, at which overheating damagecan occur on the winding insulations of the stator 41 or the electronicsystem, is reliably prevented.

LIST OF REFERENCE NUMERALS

1 Spindle housing

2 a Driven screw spindle

2 b Screw spindle in coupled motion

3 Motor housing

4 Electric motor

10 Spindle chamber

11 Pump inlet

13 Pump outlet

15 Flange section of the spindle housing

23 Shaft bearing

30 Motor chamber

31 Heat transfer section

32 Bearing seat

33 Delivery flow chamber

34 Shaft seal

35 Flange section of the motor housing

41 Stator

42 Rotor

1. An electric screw coolant pump for delivering a coolant circulationcomprising: a spindle housing having a spindle chamber in which at leasttwo screw spindles are rotatably accommodated; a pump inlet and a pumpoutlet for guiding a delivery flow through the spindle chamber; a motorhousing arranged axially adjacent to the spindle housing; wherein themotor housing includes a motor chamber in which a dry-running electricmotor is arranged so the motor chamber is delimited with respect to thedelivery flow; and the motor housing comprises a heat transfer section,through which the delivery flow flows, arranged between the motorchamber and a component boundary between the motor housing and thespindle housing.
 2. The electric screw coolant pump according to claim1, wherein the heat transfer section includes the pump outlet.
 3. Theelectric screw coolant pump according to claim 1, wherein the heattransfer section includes a delivery flow chamber that establishes aconnection between a frontal delimitation of the motor chamber and thespindle chamber.
 4. The electric screw coolant pump according to claim1, wherein the heat transfer section includes a bearing seat for a shaftbearing arranged between the electric motor and the screw spindles. 5.The electric screw coolant pump according to claim 1, wherein anelectronic system for the electric motor is arranged inside the motorchamber.
 6. The electric screw coolant pump according to claim 1,wherein a stator and/or an electronic system of the electric motor is incontact with a frontal delimitation of the motor chamber inside themotor housing.
 7. The electric screw coolant pump according to claim 1,wherein the heat transfer section is formed integrally with the motorhousing.
 8. The electric screw coolant pump according to claim 1,wherein the spindle housing is formed as one piece.
 9. The electricscrew coolant pump according to claim 1, wherein at the componentboundary between the motor housing and the spindle housing, a flangejoint is formed of a flange section of the motor housing and a flangesection of the spindle housing.